The present invention relates to a heat-sensitive ink comprising a heat-sensitive composition, which can undergo an irreversible color tone change at a predetermined temperature to thus permit the recording of whether a specific substance is exposed to a temperature higher than a predetermined level or not, as well as a heat-sensitive indicator using the same.
There have been known products, for instance, processed food products, which should be heat-treated at a temperature higher than a specific level during the manufacture of the same. There have also been known some products or articles such as products for medical use and food products, which are deteriorated, decomposed and/or putrefied, if they are exposed to a temperature higher than a specific one. In addition, there have likewise been known such products as electric equipments and electric parts, which get out of order, are broken and/or possibly cause a fire due to overheat in case of, for instance, a motor.
As a means for detecting whether a particular product experiences or is exposed to a temperature exceeding a predetermined level or not, there have conventionally been used, for instance, temperature-indicating materials capable of changing their color tone upon exposure thereof to such a predetermined temperature.
As such temperature-indicating materials, there have been known those comprising heat-fusible substances and acid-base indicators, specific examples of which are disclosed in, for instance, Japanese Patent Provisional Publication No. Sho 61-12783 and Japanese Patent Provisional Publication No. Sho 61-14284. The temperature-indicating materials of this type are reversible temperature indicators since they undergo color change upon heating and the color tone thereof is returned back to the original one when they are cooled. If a temperature-indication material of this type is used, whether a product is exposed to a temperature exceeding a predetermined level or not can be confirmed by monitoring the color tone change of the material during heating. However, if the color tone change of such a material is not monitored, it is impossible to confirm if a product experiences a temperature exceeding a predetermined level once the time elapses and the temperature of the product is reduced. Moreover, it is also impossible to record and preserve such a temperature history of the product.
In addition, Japanese Patent Provisional Publication No. Hei 10-239172 discloses a device for monitoring the upper temperature limit, which comprises a thin film of pigmented solid paraffin and a thin solid paraffin film having the same quality and deposited on the former. This device is one prepared by forming a thin film of paraffin previously pigmented and then depositing a thin film of non-pigmented paraffin on the surface of the former and should have a predetermined shape. This device is designed in such a manner that, when the device is exposed to a temperature exceeding a predetermined one, the fused upper layer or non-pigmented paraffin thin film is admixed with the lower layer or the pigmented paraffin thin film likewise in the fused state to thus develop a color tone apparently different from that observed prior to the fusion.
Moreover, Japanese Utility Model Application Publication No. Sho 46-28235 discloses an irreversible label. This label should be produced as a three-dimensional structure and therefore, the application thereof is quite limited.
Accordingly, it is a first object of the present invention to provide a heat-sensitive composition, which undergoes an irreversible color change responding to a temperature change, which permits the use of a wide variety of dyestuffs, which can be used in printing irrespective of the shape of a target to be printed, which can be mass-produced and permits the reduction of the production cost thereof and which allows the systematization of temperatures for indication or detection.
The irreversible heat-sensitive composition according to the present invention developed to achieve the first object of the present invention comprises a mixture of a granular (or granular) or powdery heat-fusible substance having a melting point corresponding to a temperature to be recorded and a granular or powdery dyestuff diffusible into the fused heat-fusible substance through dispersion or dissolution.
It is a second object of the present invention to provide a heat-sensitive ink, which can indicate, with high precision, whether it is exposed to a temperature exceeding a predetermined level or it has a desired temperature history or not, through a clear color tone change.
The heat-sensitive ink according to the present invention developed to accomplish the second object of the present invention comprises the foregoing irreversible heat-sensitive composition and an ink vehicle capable of diffusing the fused heat-fusible substance therein.
According to another embodiment of the heat-sensitive ink of the present invention comprises microcapsules in which the foregoing irreversible heat-sensitive composition is enclosed or encapsulated.
It is a third object of the present invention to provide a heat-sensitive indicator, which can indicate, with high precision, whether it is exposed to a temperature exceeding a predetermined level or it has a desired temperature history or not, through a clear color tone change which the color change itself could be preserved, and could easily be mass-produced.
The heat-sensitive indicator according to the present invention developed to achieve the third object of the invention comprises a substrate, which the foregoing heat-sensitive ink is printed on.
The irreversible heat-sensitive composition according to the present invention comprises a mixture of a granular or powdery heat-fusible substance with a granular or powdery dyestuff.
The irreversible heat-sensitive composition preferably comprises 0.001 to 100 parts by weight of the granular or powdery dyestuff per 100 parts by weight of the granular or powdery heat-fusible substance.
The heat-fusible substance is a component, which determines the color change-temperature of the irreversible heat-sensitive composition and a substance, which has, under ordinary pressure, a melting point corresponding to the temperature to be recorded and which can be fused when heated to a temperature higher than the melting point and undergo a change in state from a granular or powdery state to a liquid state. The heat-fusible substance suitably used herein is at least one member selected from the group consisting of fatty acid derivatives, alcohol derivatives, ether derivatives, aldehyde derivatives, ketone derivatives, amine derivatives, amide derivatives, nitrile derivatives, hydrocarbon derivatives, thiol derivatives and sulfide derivatives.
Specific examples of fatty acid derivatives are myristic acid, palmitic acid, adipic acid, octanoic acid, tricosanoic acid, tetratriacontanoic acid, 2,3-dimethyl nonanoic acid, 23-methyl tetracosanoic acid, 2-hexenoic acid, brassidic acid, 2-methyl-2-dodecenoic acid, xcex2-eleostearic acid, behenolic acid, cis-9,10-methylene octadecanoic acid, chaulmoogric acid, n-dodecyl 3,3xe2x80x2-thiodipropionate, trilaurin, palmitic acid anilide, stearic acid amide, zinc stearate, salicylic acid anilide, N-acetyl-L-glutamic acid, caproic acid-xcex2-naphthylamide, enanthic acid phenylhydrazide, p-chlorophenacyl arachionate, cholesteryll formate, 1-aceto-2,3-distearin, pentadecyl thiolaurate, stearic acid chloride, palmitic acid anhydride, stearic acid-acetic acid anhydride, succinic acid, sebacic acid benzyl ammonium salt, 2-bromovaleric acid, methyl xcex1-sulfostearic acid sodium salt, and 2-fluoroarachic acid.
Specific examples of alcohol derivatives are octadecyl alcohol, cholesterin, D-mannitol, galactitol, hepta-triacontanol, hexadecan-2-ol, 1-trans-2-octadecenol, xcex2-eleostearyl alcohol, cycloeicosanol, d(+)cellobiose, p,pxe2x80x2-biphenol, riboflavin, 4-chloro-2-methylphenol and 2-bromo-1-indanol.
Specific examples of ether derivatives include dihexadecyl ether, dioctadecyl ether, cytidine, adenosine, sodium phenoxyacetate, 1,3-bis (4-hydroxyphenoxy)-benzene and aluminium triethoxide.
Specific examples of aldehyde derivatives are stearin aldehyde, paralauryl aldehyde, parastearin aldehyde, naphthoaldehyde, p-chlorobenzaldehyde, phthalaldehyde and 4-nitrobenzaldehyde.
Specific examples of ketone derivatives are stearone, docoson-2-one, phenyl heptadecyl ketone, cyclononadecane, vinyl heptadecyl ketone, 4,4-bisdimethyl aminobenzophenone, bis (2,4-pentanedionite) calcium and 1-chloroanthraquinone.
Specific examples of amine derivatives include tricosylamine, dioctadecylamine, N,N-dimethyl octylamine, heptadecamethyleneimine, naphthylamine, ethyl p-aminobenzoate, o-trithiourea, sulfamethazine, guanidine nitrate, p-chloroaniline and propylamine hydrochloride.
Specific examples of amide derivatives are hexylamide, octacosylamide, N-methyl dodecylamide, N-methyl heptacosylamide, xcex1-cyanoacetamide, salicylamide, dicyandiamide, 2-nitrobenzamide and N-bromoacetamide.
Specific examples of nitrile derivatives include pentadecane nitrile, margaronitrile, 2-naphthonitrile, o-nitrophenoxy acetic acid, 3-bromobenzonitrile, 3-cyanopyridine and 4-cyanophenol.
Specific examples of hydrocarbon derivatives are hexadecane, 1-nonatriacontene, trans-n-2-octadecene, hexatriacontyl benzene, 2-methylnaphthalene, picene, cyanuric chloride, 1-fluorononadecane, 1-chloroeicosane, 1-iodopentadecane, 1-bromoheptadecane and 1,2,4,5-tetrakis (bromomethyl) benzene.
Specific examples of thiol derivatives are pentadecane thiol, eicosane thiol, 2-naphthalene thiol, 2-mercaptoethyl ether and 2-nitrobenzene sulfenyl chloride.
Specific examples of sulfide derivatives are 1,3-diatine, 2,11-dithia [3,3] paracyclophane, bis (4-hydroxy-3-methylphenyl) sulfide, 4,4-dipyridyl sulfide and 4-methyl mercaptophenol.
This heat-fusible substance preferably has a particle size ranging from 0.01 xcexcm to 5 mm.
The dyestuff is included in the irreversible heat-sensitive composition in the form of granules or powder and can diffuse into the fused heat-fusible substance through dispersion or dissolution. Alternatively, the dyestuff may likewise be one such that the surface of the dyestuff granule or powder is wetted with the fused heat-fusible substance and changed to a wet color. The dyestuff may be selected from wide variety of dyestuffs, for instance, dyes such as direct dyes, acid dyes, basic dyes, disperse dyes, reactive dyestuffs, oil-soluble dyes, vat dyes, mordant dyes, azo dyes and sulfide dyes; pigments such as organic pigments and inorganic pigments; and pigmented substances. These dyestuffs may be used alone or in any combination of at least two of them.
Specific examples of dyes include C.I. Direct Orange 39, C.I. Direct Brown 2, C.I. Acid Yellow 73, C.I. Acid Red 52, C.I. Acid Violet 49, C.I. Basic Yellow 11, C.I. Basic Red 38, Cathilon Red GTLH, Cathilon Red 4GH, Cathilon Red 7BN11 and Cathilon Red SGLH (available from Hodogaya Chemical Co., Ltd.); C.I. Mordant Red 7, C.I. Mordant Black 38, C.I. Azoic Blue 9, C.I. Azoic Diazo Component 11, C.I. Sulfur Black 1, C.I. Sulfur Red 5, C.I. Vat Green 9, C.I. Vat Violet 2, C.I. Disperse Blue 3 and Discharge Red BB (available from Mitsui Toatsu Dyes Co., Ltd.); C.I. Reactive Blue 19, C.I. Reactive Blue 15 and Remazol Br Blue R-KN (available from Mitsubishi Chemical Industries, Ltd.); C.I. Solvent Orange 2, C.I. Solvent Blue 25, C.I. Acid Green 1, Flavianic Acid Disodium Salt and Primuline Sulfonic Acid.
Specific examples of organic pigments are 4,10-dibromoanthanthrone, dibenzoanthrone, cochineal lake, C.I. Pigment Yellow 1, C.I. Pigment Red 38, C.I. Pigment Blue 15, C.I. Pigment Red 209, C.I. Pigment Yellow 109, C.I. Pigment Green 10, C.I. Basic Red 1-Lake, C.I. Acid Red 87-Lake, C.I. Pigment Blue 6, C.I. Pigment Red 179, C.I. Pigment Red 88, Alizarin Lake, C.I. Pigment Violet 23, C.I. Pigment Green 8, C.I. Pigment Red 53, C.I. Pigment Yellow 23-Lake, tannic acid-gallic acid-iron lake, C.I. Pigment Yellow 34 and C.I. Pigment Yellow 35. In this connection, the foregoing term xe2x80x9cC.I.xe2x80x9d is an abbreviation of xe2x80x9ccolor indexxe2x80x9d.
Specific examples of inorganic pigments are kaolin, Prussian blue, strontium sulfate, titanium dioxide, aluminum hydroxide, calcium silicate and carbon black.
The dyestuff preferably has a particle size ranging from 0.001 xcexcm to 5 mm.
In the irreversible heat-sensitive composition, the granular or powdery heat-fusible substance and the granular or powdery dyestuff are in a mixed state, the dyestuff is covered up with the heat-fusible substance and the granular or powdery heat-fusible substance is fused, while the granular or powdery dyestuff is dispersed or dissolved in or wetted with the fused heat-fusible substance to thus cause a color tone change when the temperature reaches or exceeds a desired level. After the color tone change, it is never returned back to the original color tone even if the composition is cooled and the heat-fusible substance is solidified.
To obtain this irreversible heat-sensitive composition, a heat-fusible substance and a dyestuff are mixed together in a desired mixing ratio, followed by pulverization of the resulting mixture to a desired particle size; or the foregoing two components are separately pulverized to a desired particle size and then the pulverized components are mixed together in a desired mixing ratio.
The heat-sensitive ink according to the present invention comprises the foregoing irreversible heat-sensitive composition comprising a mixture of a granular or powdery heat-fusible substance having a melting point corresponding to a temperature to be recorded and a granular or powdery dyestuff diffusible into the fused heat-fusible substance through dispersion or dissolution; and an ink vehicle capable of diffusing the fused heat-fusible substance therein.
The ink vehicle does not permit any dissolution or diffusion of the heat-fusible substance and the dyestuff at ordinary temperature, but permits the diffusion of the fused substance in which the dyestuff is dispersed or dissolved. The ink vehicle may be, for instance, acrylic resins, phenol resins, nylon, ethyl cellulose, hydroxymethyl cellulose, polyvinyl alcohol and carboxymethyl cellulose. The ink vehicle may likewise be any commercially available ink vehicles such as PAS800 Medium (the trade name of a product available from Jujo Chemical Industry Co., Ltd.) and High Set Mat Medium (the trade name of a product available from Mino Group K.K.).
It is preferred that the heat-fusible substance be included in the heat-sensitive ink in an amount ranging from 10 to 70% by weight. This is because if the amount thereof is less than 10% by weight, the resulting color tone change is insufficient or indistinct, while if it exceeds 70% by weight, the adhesive force of the resulting ink is too low to coat or print a substrate with the ink.
This heat-sensitive ink may comprise a solvent, which does not dissolve the heat-fusible substance and the dyestuff, but can dissolve the ink vehicle. Such a solvent may be, for instance, water, ethanol, butanol, ethyl acetate, isoamyl acetate, methyl ethyl ketone, methyl isobutyl ketone, xylene, diethyl benzene, toluene, butyl cellosolve, ethyl cellosolve and mineral spirit.
This heat-sensitive ink can be prepared by uniformly kneading, in a kneader, the foregoing heat-fusible substance and dyestuff, which are pulverized to a desired particle size, an ink vehicle and a solvent.
According to another embodiment of the heat-sensitive ink of the present invention may comprise microcapsules each of which encloses the foregoing irreversible heat-sensitive composition comprising a mixture of a granular or powdery heat-fusible substance having a melting point corresponding to a temperature to be recorded and a granular or powdery dyestuff diffusible into the fused heat-fusible substance through dispersion or dissolution. The microcapsules are unevenly distributed in the resulting ink.
The microcapsule is, for instance, a minute particle having a uniform outer wall and having a size ranging from about 0.01 xcexcm to about 10 mm, which encloses the granular or powdery dyestuff and heat-fusible substance.
In the present invention, it is preferred that the outer wall of the microcapsule be formed from a polymer compound selected from the group consisting of polyvinyl alcohol, polystyrene, silicone resins, epoxy resins, acrylic resins, urea resins, gelatin, methyl cellulose, polyurethane, waxes, gum arabic, dextrin, and nylon.
Such microcapsules are, for instance, prepared by an interfacial polymerization method, an in-situ production method, a phase separation method, a suspension-in air method, an electrostatic coalescence method, a spray coagulation method and a drying-in liquid method.
The microcapsules are preferably contained in the heat-sensitive ink in an amount ranging from 10 to 70% by weight. This is because if the amount thereof is less than 10% by weight, the color tone change of the resulting ink is insufficient or indistinct, while if it exceeds 70% by weight, the adhesive force of the resulting ink is too low to coat or print a substrate with the ink.
The use of the microcapsules permits the improvement of not only the stability of the heat-fusible substance and the dyestuff present in the ink, but also the environmental resistance of the ink. Moreover, in the preparation of the ink, vehicles and solvents to be incorporated into the ink are not restricted to those, which do not dissolve the heat-fusible substance and the dyestuff and the resulting ink is excellent in the printability and the storage stability after printing.
The heat-sensitive ink preferably comprises an ink vehicle identical to those described above. The ink vehicle may be commercially available ones other than those listed above such as Aqua Set Ink (the trade name of a product available from Jujo Chemical industry Co., Ltd.), VAR-000 Medium (the trade name of a product available from Teikoku Ink K.K.) and Ramistar R Medium (the trade name of a product available from Toyo Ink Mfg. Co., Ltd.).
This heat-sensitive ink may comprise a solvent capable of dissolving the ink vehicle. This solvent may be isopropyl alcohol in addition to those listed above.
This heat-sensitive ink can preferably be prepared as follows: First, microcapsules are prepared according to the interfacial polymerization method. More specifically, a heat-fusible substance and a dyestuff are dispersed or emulsified in a solvent which does not dissolve the heat-fusible substance and the dyestuff, but can dissolve a polymeric compound for forming the outer wall of the microcapsules using a device such as a stirring machine, a disperser, a homogenizer or a mixer. Then an emulsifying-hardening agent is added to the resulting dispersion to thus form the outer wall of the microcapsules and thereafter the resulting microcapsules are separated from the solvent by, for instance, filtration to thus give desired microcapsules in which the heat-fusible substance and the dyestuff are enclosed. Finally, an ink vehicle, a solvent for ink vehicle and the resulting microcapsules are kneaded in a kneader to give a heat-sensitive ink.
In this respect, the heat-sensitive ink may further comprise a dispersant for improving the dispersibility of the dyestuff and for making the color tone change of the ink more distinct, such as talc, magnesium carbonate and silica. In order to make the color tone change more distinct, the heat-sensitive ink may optionally comprise at least one member selected from the group consisting of dyes such as direct dyes, acid dyes, basic dyes, disperse dyes, reactive dyestuffs, oil-soluble dyes, vat dyes, mordant dyes, azo dyes and sulfide dyes; pigments such as organic pigments and inorganic pigments, which are auxiliary coloring agents showing colors contrast to the color tone of the dyestuff. Moreover, the heat-sensitive ink may likewise comprise a wax and/or a surfactant for controlling the flowability and the drying characteristics of the ink.
The heat-sensitive indicator according to the present invention comprises a substrate and a printed layer of the foregoing heat-sensitive ink, which is applied onto the surface of the substrate and comprises an irreversible heat-sensitive composition, which is a mixture of a granular or powdery heat-fusible substance having a melting point corresponding to a temperature to be recorded and a granular or powdery dyestuff diffusible into the fused heat-fusible substance through dispersion or dissolution, and an ink vehicle capable of diffusing the fused heat-fusible substance therein.
According to another embodiment of the present invention, the heat-sensitive indicator comprises a substrate and a printed layer of the foregoing heat-sensitive ink, which is applied onto the surface of the substrate and comprises microcapsules each of which encloses the irreversible heat-sensitive composition comprising a mixture of a granular or powdery heat-fusible substance having a melting point corresponding to a temperature to be recorded and a granular or powdery dyestuff diffusible into the fused heat-fusible substance through dispersion or dissolution.
Examples of such substrates are paper such as plain paper, Japan art paper and Kent paper; synthetic paper; wood such as sun tree timber; and plastic substrates such as polypropylene, polyethylene terephthalate, acrylonitrile-butadiene-styrene resin, polycarbonate and acrylic resin substrates.
These heat-sensitive indicators may be in the form of a card-like, sheet-like or rod-like shape. Alternatively, they may be labels, which carry an adhesive layer on the back face.
The printing of the substrate with the heat-sensitive ink is performed by, for instance, screen-printing, offset printing, gravure printing and brush coating techniques.
The ink layers formed on the substrate by printing with these heat-sensitive inks may be covered up with a transparent or translucent laminate material made of a resin. Examples of such laminate materials are plastic films such as polypropylene, polyethylene terephthalate, acrylonitrile-butadiene-styrene resin, polycarbonate and acrylic resin films; and printing mediums for laminate such as acrylic resins, nylon and phenol resin.
In these heat-sensitive indicators, the heat-fusible substance and the dyestuff are in a mixed state, prior to heating. If the indicator is heated to a temperature higher than the melting point of the heat-fusible substance, however, the dyestuff diffuses into the fused heat-fusible substance through dispersion or dissolution or the surface of the granular or powdery dyestuff is wetted with the fused heat-fusible substance so that the indicator undergoes a desired color tone change. Alternatively, in case of the indicator, which makes use of microcapsules, the heat-fusible substance and the dyestuff enclosed in the microcapsules may be permeated through the outer wall of the microcapsules and diffuse into the ink vehicle, after the fusion of the heat-fusible substance by heating.
This diffusion of the foregoing components is irreversible. Therefore, once the indicator undergoes a desired color tone change, the color tone thereof is never returned back to the original one even if the heat-fusible substance is cooled, after the color tone change, and solidified.
When practically using these heat-sensitive indicators, they are arranged near the product of which temperature history is to be detected or they are adhered to such a product. Alternatively, it is also possible to directly print such a product with the heat-sensitive ink.